If you are going to use separate shelf stacks for each of the new and old controllers, I think an easy way to do this would be by cascading the snapmirrors. Like, SG old -> HK old -> SG new -> HK new. That way you can avoid a resync. If you are planning to continue with HK old, after HK old -> SG new, you may have to do a snapmirror reverse resync. Please see "Data Protection Online Backup and Recovery Guide" at https://library.netapp.com/ecm/ecm_download_file/ECMP1196991 for supported configurations.
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